1. Field of the Invention
The present invention relates to non-impact printer apparatus for recording, and more specifically, to circuitry thereon for controlling data and other signals flowing to a printhead forming part of the printer apparatus.
2. Description of the Prior Art
In U.S. Pat. No. 4,746,941, a grey level LED (light emitting diode) printhead is described. In a printhead of the type described therein, signals comprising plural digital data bits representing a time for recording a pixel (picture element) are simultaneously fed to the printhead over a data bus. A token bit is also provided simultaneously with the data to activate certain latch registers associated with a respective LED so that the data is distributed appropriately. As noted in this patent, the use of the token bit simplifies circuitry and connection pads on the printhead and thereby facilitates construction of the printhead.
In U.S. Pat. No. 4,885,597, an LED printhead is described wherein compensation for age and temperature of the LED's is accommodated to ensure that the intensity from the LED's is consistent over time. In this printhead, current to the LED's is regulated using digitally addressable current mirrors associated with each driver chip. The multi-bit digital signals used must be communicated to the driver chips.
In a highly productive printer apparatus there is insufficient time available to feed signals in serial fashion. While this simplifies printhead structure, productivity suffers. The requirement of additional signals for current regulation adds complexity to the structure and requires still more lines and connection pads.
It is therefore an object of the invention to provide an improved printhead with efficient means for handling data and other signals for controlling current to the recording elements.